Patient-Ventilator Interaction During Acute Lung Injury, and the Role of Spontaneous Breathing: Part 1: Respiratory Muscle Function During Critical Illness

Abstract

SummarySince the early 1970s there has been an ongoing debate regarding the wisdom of promoting unassisted spontaneous breathing throughout the course of critical illness in patients with severe respiratory failure. The basis of this debate has focused on the clinical relevance of opposite problems. Historically, the term "disuse atrophy" has described a situation wherein sustained inactivity of the respiratory muscles (ie, passive ventilation) results in deconditioning and weakness. More recently it has been referred to as "ventilator-induced diaphragmatic dysfunction." In contrast, "use atrophy" describes a situation where chronic high-tension inspiratory work causes structural damage to the diaphragm and weakness. Both laboratory and clinical studies demonstrated that relatively brief periods of complete respiratory muscle inactivity, as well as intense muscle loading, result in acute inflammation, loss of muscle mass, and weakness. Yet in critical illness other factors also affect respiratory muscle function, including prolonged use of neuromuscular blocking agents, administration of corticosteroids, and sepsis. This makes the attribution of acquired respiratory muscle weakness and ventilator-dependence to either ventilator-induced diaphragmatic dysfunction or loaded breathing extremely difficult. Regardless, the clinical implications of this research strongly suggest that passive mechanical ventilation should be avoided whenever possible. However, promotion of unassisted spontaneous breathing in the acute phase of critical illness also may carry a substantial risk of respiratory muscle injury and weakness. Use of mechanical ventilation modes in a manner that induces spontaneous breathing effort, while simultaneously reducing the work load on the respiratory muscles, is probably sufficient to minimize both problems. Key words: acute lung injury; acute respiratory distress syndrome; discoordinated breathing; disuse atrophy; respiratory muscle fatigue; ventilator-induced diaphragmatic dysfunction; use atrophy. [Respir Care 2011;56(2):181-189.

Variability in Mechanical Ventilation: What's All the Noise About?

“…47 Both patient-triggered ventilation and spontaneous ventilation facilitate better ventilation/perfusion matching, reduce ventilator-induced lung injury, and preserve diaphragmatic function. [48][49][50] Furthermore, patient-triggered ventilation modes can potentially yield a highly variable respiratory pattern, akin to the experimental variable ventilation studies reported previously. Multiple modes of patient-triggered ventilation are currently available, and the respiratory therapist should utilize the most familiar mode.…”

Sequential invasive-noninvasive mechanical ventilation weaning strategy for patients after tracheostomy

“…At this time, sputum expectoration markedly reduced, severe respiratory failure was corrected, but there were somewhat respiratory muscle fatigue and respiratory dynamic abnormality. [29,30] Non-invasive positive pressure ventilation is more conducive to the recovery of respiratory muscle fatigue. [31] Luo et al [32] provide experimental evidence that most AECOPD patients can breathe independently at the pulmonary infection control window, but develop respiratory distress and noninvasive positive pressure ventilation is required after extubation.…”

Patient-Ventilator Interaction

“…As part of his presentation on airway pressure release ventilation (APRV), Rich Kallet reviewed this topic for us in depth. 12 Although his presentation fell on the second day of the conference, respiratory muscle function is sufficiently important to all the topics under consideration that I will address it here. Many studies in patients with COPD and neuromuscular disease have shown that mechanical loads in excess of what the respiratory muscles can sustain continuously will lead to electromechanical abnormalities, physical signs such as paradoxical chest and abdominal motion, and, ultimately, overt ventilatory failure.…”

“…Along with the bedside manifestations of excessive respiratory muscle effort is accumulating evidence that excessive stress on these muscles is both functionally and anatomically damaging to them. 12 An understandable response to the distress patients may experience due to PVA is to try to "take them out of the equation" by means of heavy sedation-sometimes with the addition of pharmacologic paralysis-and rendering them completely passive during ventilatory support. However, passive mechanical ventilation is also now known to be detrimental to the respiratory muscles, producing detectable diaphragmatic dysfunction after as little as 48 hours of inactivity, and frank muscle atrophy when prolonged (Fig.…”

“…This paper summarizes what I took to be the most important messages of the individual presentations and the discussions that followed them, and offers some of my own observations on this central component of the management of patients with acute respiratory failure. With a few exceptions I will not attempt to cite the most important primary work that has been done in this field; the individual papers in these 2 special issues [1][2][3][4][5][6][7][8][9][10][11][12][13][14] provide a comprehensive and authoritative review of the literature pertaining to PVI.…”